Negative Refractive Materials Research Articles

Bilateral Symmetric non-Euclidean multi-frequency invisibility

Light propagation in non-Euclidean geometry has become a hot topic in recent years, while transformation optics theory demonstrates unique advantages in this respect. A notable application of transformation optics in non-Euclidean space is non-Euclidean invisibility cloak which avoids the challenges of negative refraction and anisotropic materials. In this work, we propose another configuration for non-Euclidean invisibility, capable of achieving invisible across a wide spectrum. Using coordinate transformation, we convert this non-Euclidean invisibility into planar gradient medium and validate its effects through full wave simulations. We also discover that the corresponding gradient medium can further relax the material parameters. Our findings suggest diverse strategies for non-Euclidean invisibility and planar gradient media, potentially advancing optical invisibility and transformation optics in non-Euclidean spaces.

Ultra-narrowband circular dichroism in all-dielectric chiral nanohole arrays based on griddings and monolayer MoS2

The strong circular dichroism (CD) of metallic chiral nanostructures can be applied to polarization conversion, negative refraction materials, and chiral molecule detection. However, metallic chiral nanostructures with losses struggle to produce dynamically tunable ultra-narrow band circular dichroism signals, which greatly limits their applications in sensing. In this paper, the MoS2 and Sb2S3 with phase change characteristics are introduced into all-dielectric chiral nanopore arrays (ACNAs) based on gridding to generate dynamically tunable ultra-narrow band circular dichroism signals. Simulation results show that ACNAs/MoS2 produce two strong narrow-band CD signals in the visible range. The maximum CD intensity can reach 0.75, and the maximum half-width can reach 0.8 nm. The electric field distribution indicates that two CD signals are mainly caused by the guided mode resonance. The ultra-narrow band CD signals both lie on their geometric parameters and can realize the dynamic regulation by changing the incidence angle of lights and the crystalline state of Sb2S3. Furthermore, the sensing characteristics of this device were evaluated by analyzing the effects of different concentrations of SARS-CoV-2 solutions on the CD spectra. These findings will facilitate the design of all-dielectric chiral nanostructures with dynamically tunable ultra-narrow band CDs and facilitate their applications in biosensing.

Direct stress minimization in electro‐mechanical metamaterials

AbstractMetamaterials are artificially created multiscale materials with many different applications [1]. We assume periodic microstructure. No specific length scale is demanded for the differentiation between the scales. Instead, we consider the microscale as consisting of repeating unit cells, whereas the macroscale is the scale, where desired and sometimes unusual physical effects occur. The precise arrangement and geometry at the microscale level is responsible for the macroscopic material behavior, which can substantially differ from the original components it is made from. This way, unique material properties otherwise not found in nature (e.g. negative refractive materials [2]) are possible. Most previous research regarding metamaterials concentrated only on a single physical branch in each case, e.g. electromagnetic or acoustic metamaterials [3,4].In this contribution we present a class of theoretical electro‐mechanical metamaterials by combining insulating and conducting materials. Our aim is to directly control and reduce the resulting total stress of insulating materials by counteracting the mechanical stress through the application of an electric field, which is created by a conducting material. The solution of the resulting minimization problem is related to the eigenvalues of the mechanical stress tensor. Additionally, we discuss the constrained cases of tension and compression and cover the plane stress case. We show numerical results for all cases and discuss the limits of such a material.

Modulation instability solitons in oppositely double-doped directed couplers with two negative refractive index material channel and non-Kerr nonlinearity

In a three-core nonlinear contrarily directed coupler with two negative-index material channels, we theoretically explore the instability in the presence of a non-Kerr-like nonlinear refractive-index shift. Through the use of linear stability analysis, we determine an expression for the instability gain. It is discovered that the septic saturation, the ratio of the forward- to backward-propagating wave power, pump power, and nonlinearity all have a substantial impact on the MI in the nonlinear three-core contrarily directed coupler. The septic and saturation nonlinearity is found to improve the MI in the case of forward-to-backward ratio power (f) by boosting the width and gain of the instability profile in both normal and abnormal dispersion regimes. However, septic nonlinearity improves the MI in the case of pumps by boosting both its width gain and in the abnormal dispersion regime alone. Using 2D pictures, we could investigate the MI's dynamic behaviour during an anomalous dispersion regime. We discovered from the contour images that the gain of the instability profile grows as septic and saturation nonlinearity increases in both normal and abnormal dispersion regimes. So, with a focus on a negative refractive material channel in the existence of contamination and saturation nonlinearity, we report new techniques for producing and controlling MI and soliton in three-core contrarily directed couplers.

Prediction of negative refraction in Dirac semimetal metamaterial

Negative refraction materials are indispensable building blocks in the optoelectric devices for their unique functionalities of controlling the light propagations, such as, superlens and transformation optics. However, material realizations of negative refraction are still limited to the conventional metals, semiconductors as well as magnetic materials. Here, we show that three dimensional Dirac semimetals have the opportunity to enable the negative refraction, which can be achieved through alternatively stacking three dimensional Dirac semimetals and the dielectric layers together. It is found that the effective perpendicular and parallel permittivities in this multilayered stack display the respective negative and positive values over a certain frequency region, which enables its negative group refractive angle and it can be controlled by the Fermi energy of Dirac semimetals. The spectra of transmittance in the multilayered structure for transverse magnetic wave also reveals an incident angle-independent transmittance dip, which originates from the zero value of the real part of the effective perpendicular permittivity. Our findings unveil the essential role of three dimensional Dirac semimetals in producing the negative group refraction responses and promise their applications in the metamaterial-based devices.

Architected material analogs for shape memory alloys

Architected material analogs for shape memory alloys

Plate arrays as a perfectly-transmitting negative-refraction metamaterial

A closely-spaced periodic array of identical thin rigid plates illuminated by incident waves is shown to exhibit properties of a negative refraction metamaterial under certain conditions. The close-spacing assumption is used as a basis for an approximation in which the region occupied by the plate array acts as an effective medium. Effective matching conditions on the plate array boundary are also derived. The approximation allows explicit expressions to be derived to wave scattering problems involving tilted plate arrays. This approximation is tested for its accuracy against an exact treatment of the problem based on Bloch–Floquet theory.Both the exact and effective medium theory predict perfect wave transmission at all wave frequencies through the array when the tilt angle of plates in the array is the reverse of the incident wave direction: the array acts as an all-frequency perfectly-transmitting negative-refraction medium. For certain frequencies the array is also shown to act as an all-angle perfectly-transmitting negative-refraction material.

Smart Materials Vis-à-vis Metamaterials

Smart materials are custom-designed materials that have certain properties that can undergo significant changes as guided through external influence, such as pressure, temperature, pH, electric or magnetic fields. One of the most amazing developments in the smart materials is that of metamaterials. The origin of Meta stems from Greek meaning “beyond”. Metamaterials have rare properties not found in natural occurring materials such that their properties are based on their structure rather than material of their composition. These materials find applications in many fields like public safety, sensors, battlefield communication, ultrasonic devices, solar power equipments, and remote aerospace applications. A synthetic composite material with a structure such that it possesses properties being unusual in natural materials specially a negative refractive index-these materials scatter electromagnetic wave unlike any known material. Thus the shape of the wave emerging from the metamaterials is entirely different from a conventional wave. Besides having a myriad of applications, these materials have the remarkable ability to bend light which can make airplanes, tanks and submarines invisible resulting in the epitome of stealth capability. Metamaterials now find recognition as an enabling technology being the most exciting research area at the crossroads between photonics and nanoscience. Without any exaggeration, the present era is the century of metamaterials. This paper, inter alia, highlights the significance of metamaterials in general and its stealth capabilities for defence sector in particular.

Low-Loss Left-Handed Gammadion-Fishnet Chiral Metamaterials

Negative refraction has many potential applications in the information and communications technology field. However, the high losses of most negative refraction materials prevent the use of this novel property in the implementation of practical devices in the HF range. In an attempt to overcome this inconvenience, we present two gammadion–fishnet chiral metamaterial structures, constituted by the combination of a lossy chiral metamaterial and different fishnet structures. The electromagnetic characterization of the proposed metamaterials provides a larger bandwidth with negative refraction as well as lower losses when compared with the initial structures. The results were obtained by using both numerical and experimental data, which support our designs.

Terahertz super-resolution imaging using four-wave mixing in graphene

A perfect lens made from negative refraction (NR) materials is utilized to overcome the diffraction limit. However, these NR lenses are realized by metamaterials, which suffer from high losses, and the volume is bulky. In this Letter, we propose a terahertz NR lens by using a four-wave mixing (FWM) process in graphene. NR is demonstrated because of the phase matching along the surface of graphene. Evanescent waves that store high spatial frequency information can be converted into propagating waves in the nonlinear NR process. An image with subwavelength resolution is reconstructed at the FWM wavelength. Theoretical analysis and numerical simulations are performed to demonstrate the capability of such imaging. The lens has a subwavelength resolution of around λ/5. The lens needs low field intensity due to the strong nonlinear response of graphene in the terahertz frequency. This Letter may have applications in terahertz microscopy.

Can researchers make a perfect optical lens?

Perfect lens can break the diffraction limit by amplifying evanescent wave components emitted from objects and enable subwavelength imaging, which may potentially lead to the revolution of modern imaging technologies. This ground breaking feature has challenged the well-accepted wisdom on the role of evanescent waves in imaging, which has generated significant research interest from the scientific communities across different disciplines. However, it was also being strongly disputed at the beginning. The implementation of this lens would be technically rather difficult and challenging due to the absolute requirement of negative refractive indexed materials that are not available in nature. Artificial electromagnetic materials, widely known as metamaterials, with both electric and magnetic responses have been then proposed to simultaneously generate negative permittivity and permeability constants. Because of the issues of fabrication and loss, the perfect-lens effect was first demonstrated only in microwaves by a two-dimensional transmission line experiment using lumped circuit design with left-handed properties. For optics, which is more anticipated for applications, alternative lens designs have been developed to manipulate evanescent waves in different ways and also create subwavelength imaging. Design and experimental techniques and methodology have been intensively discussed in the literature to improve the fabrication efficiency and device performance. Significant progress has been achieved on subwavelength imaging inspired by the employment of metamaterials. However, there are still critically important technical or physical issues unsolved for all of the subwavelength lens scenarios proposed so far, which demand innovative ideas. In particular, it is still an unknown question that whether a perfect lens with negative refractive index could be made in optics. The promising future is indicated by the recent progress on the experiment for the fabrication of high-quality negative refractive index metamaterials. In this paper, from the historical and progressive aspects of perfect lens, we describe the perspective and outlook based on a survey of the available analysis of parametric and technological challenges imposed by this special lens.

Overlapping illusions by transformation optics without any negative refraction material.

A novel method to achieve an overlapping illusion without any negative refraction index material is introduced with the help of the optic-null medium (ONM) designed by an extremely stretching spatial transformation. Unlike the previous methods to achieve such an optical illusion by transformation optics (TO), our method can achieve a power combination and reshape the radiation pattern at the same time. Unlike the overlapping illusion with some negative refraction index material, our method is not sensitive to the loss of the materials. Other advantages over existing methods are discussed. Numerical simulations are given to verify the performance of the proposed devices.

Bulk plasmon-polariton gap solitons in defective metamaterial photonic superlattices.

We show the existence of a defect mode within the plasmon-polariton gap in 1D defective photonic superlattices, composed by alternating layers of conventional dielectric (A) and negative refractive (B) material slabs with a dielectric defective layer (D), which, in the nonlinear regime, can be tuned by means of the incident field intensity. Also, we have shown that the self-induced transparency phenomena can be only observed when gap-soliton modes, coupled through the defective layer, are excited in both mirror systems around the defective slab.

Novel method of detecting movement of the interference fringes using one-dimensional PSD.

In this paper, a method of using a one-dimensional position-sensitive detector (PSD) by replacing charge-coupled device (CCD) to measure the movement of the interference fringes is presented first, and its feasibility is demonstrated through an experimental setup based on the principle of centroid detection. Firstly, the centroid position of the interference fringes in a fiber Mach-Zehnder (M-Z) interferometer is solved in theory, showing it has a higher resolution and sensitivity. According to the physical characteristics and principles of PSD, a simulation of the interference fringe’s phase difference in fiber M-Z interferometers and PSD output is carried out. Comparing the simulation results with the relationship between phase differences and centroid positions in fiber M-Z interferometers, the conclusion that the output of interference fringes by PSD is still the centroid position is obtained. Based on massive measurements, the best resolution of the system is achieved with 5.15, 625 μm. Finally, the detection system is evaluated through setup error analysis and an ultra-narrow-band filter structure. The filter structure is configured with a one-dimensional photonic crystal containing positive and negative refraction material, which can eliminate background light in the PSD detection experiment. This detection system has a simple structure, good stability, high precision and easily performs remote measurements, which makes it potentially useful in material small deformation tests, refractivity measurements of optical media and optical wave front detection.

Left-Handedness with Three Zero-Absorption Windows Tuned by the Incoherent Pumping Field and Inter-Dot Tunnelings in a GaAs/AlGaAs Triple Quantum Dots System**Supported by the National Natural Science Foundation of China under Grant No 61205205, and the Foundation for Personnel Training Projects of Yunnan Province under Grant No KKSY201207068.

Left-handedness with three zero-absorption windows is achieved in a triple-quantum-dot system. With the typical parameters of a GaAs/AlGaAs heterostructure, the simultaneous negative relative electric permittivity and magnetic permeability are obtained by the adjustable incoherent pumping field and two inter-dot tunnelings. Furthermore, three zero-absorption windows in the left-handedness frequency bands are observed. The left-handedness with zero-absorption in the solid state heterostructure may solve the challenges not only in the left-handed materials achieved by the photonic resonant scheme but also in the application of negative refractive materials with a large amount of absorption.

饱和非线性效应对负折射材料中孤子自频移的影响

饱和非线性效应对负折射材料中孤子自频移的影响

Topology optimization of multilayer left-handed material based on the genetic algorithm

Owing to the special properties, left-handed materials (LHM) have important potential applications in engineering. However, in the current stage, the design of LHM is primarily based on several basic prototypes such as meta-material and transmission line structures. In the present work, the topology optimization technology is introduced to design a type of multilayer LHM. A type of one-dimensional material with periodic unit cell is studied and the topology of its microstructure is designed by using the technology of enumerative search and genetic algorithm (GA), respectively. The material is composed of metal and ferrite films, and several types of negative refraction materials are obtained numerically. These obtained materials with periodic unit cells can exhibit negative refractive index in some frequency spectrums, and the results show that the GA could achieve good designs efficiently in a larger design space.

Conditions of Perfect Imaging in Negative Refraction Materials with Gain

Light propagation is analyzed in a negative refraction material (NRM) with gain achieved by pumping. An inherent spatial “walk-off” between the directions of phase propagation and energy transfer is known to exist in lossy NRMs. Here, the analysis is extended to the case where the NRM acts as an active material under various pumping conditions. It is shown that the condition for perfect imaging is only possible for specific wavelengths under special excitation conditions. Under excessive gain, the optical imaging can no longer be perfect.

Modulation instability in negative refractive materials with saturable nonlinearity

Starting directly from the nonlinear propagation equation including saturable nonlinearity, the first- and the second-order nonlinear dispersions, the dispersion relation, instable condition, gain spectra, and the dimensionless cut-off frequency and gain spectra of modulation instability (MI) in the negative refractive material are deduced by adopting the linear stability analysis and Drude electromagnetic model. And the variations of the dimensionless gain spectra with the normalized angular frequency and normalized incident power are calculated and discussed for different sign relations between the linear dispersion and the third-order nonlinear coefficients. The results show that in the negative refractive index region, MI can occur irrespective of the sign relation between the linear dispersion and the third-order nonlinear coefficients. And depending on different dimensionless angular frequencies and different sign relations, the variations of the dimensionless gain spectra with incident power take on several different forms. Namely, the peak gain and the cut-off frequency of MI may increase then decrease with the increase of the incident power, or decrease monotonously. Moreover, MI may even have a threshold incident power for some cases.

Negative refraction with absorption suppressed by electromagnetically induced transparency in a left-handed atomic system

This paper intends to realize negative refraction with absorption suppressed by the electromagnetically induced transparency (EIT) in a dense four-level atomic system. Without the two equal transition frequencies responding to the probe field, the atomic system displays a negative refraction with the simultaneously negative permittivity and negative permeability (left-handedness). The response of the probe field is amplified and propagates transparency in some frequency extents. Therefore, our aim for searching the low-loss negative refraction can be achieved in the scheme, given the main applied limitation of the negative refractive materials is the large amount of dissipation and absorption. However, an excessive signal field intensity would increase the absorption near the resonance in our scheme.